In a move that is unlikely to be remembered as Robbie Williams's most romantic, the singer has formally denied that he is betrothed to his long-time girlfriend. The announcement comes just days after Williams popped the question on an Australian radio show – and contradicts the proud news reported by his own poor mum.

"Hey all," Williams posted on his website on Saturday. "We are not engaged. Rob." His publicist's message was equally terse, saying simply: "We have no more comment on this apart from to confirm that they are not engaged."

These denials mark an abrupt change of events from Friday, when Williams asked Ayda Field if she would "mind being my betrothed for the end of time". Worse, they contradict made comments by Jan Williams, Robbie's mother, who told BBC 5 Live that the singer had told her "a week ago" that he planned to ask Field to marry him.

The fuss began on Australian breakfast show 2Day FM, when host Jackie Henderson told Williams that Sydney has a reputation for celebrity marriage proposals. The former Take That star then turned to Field, 35, and said: "Ayda Field, I love you so much. Do you mind being my betrothed for the end of time?" She laughed before replying, "I would love to be your betrothed 'til the end of time".

This on-air exchange unleashed a torrent of congratulatory phonecalls from Australian fans. Williams accepted them blithely, borrowing a ring from Henderson and slipping it on to Field's finger. But Williams's spokesperson later called it a "joke" and the singer himself admitted he told "a lie" some time that morning.

If the proposal was a joke, someone should have alerted Robbie's mum. Jan Williams told the BBC she had "always wanted a daughter-in-law" and was "very excited" for the couple. "They've been together for nearly three years, so it's about time," she said. "She's a great mate, as well as a lover. She's got all the qualities that he needs in a girl. It's a lovely match." Though Robbie has made the betrothal seem like an off-the-cuff gag, his mother said it was no such thing – and that he had already bought an engagement ring. As for the wedding itself, Jan Williams remarked, "I don't think it will be that far in the not-too-distant future."

Robbie certainly seemed enthusiastic in a recent interview with Jonathan Ross. "She's a wonderful person and I'm in love," he said. Despite always thinking he was "going to be a bachelor ... I was introduced to Ayda and things just changed." It seems that this weekend they, er, changed again.